Crumble

With a final word and gesture, time takes control of the object, eroding it away before your eyes, aging it several centuries in a few seconds.

(Spell Compendium, p. 56)  
Originally posted on D&D tools

Transmutation

Level: Druid 3,
Components: V, S,
Casting Time: 1 standard action
Range: Medium (100 ft. + 10 ft./level)
Target: One structure or construct
Duration: Instantaneous
Saving Throw: Fortitude half (object)
Spell Resistance: Yes (object)

You bring the forces of erosion to bear on a fabricated structure such as a stone, bridge, a wooden building, an iron wall, a construct, or any other object not formed by nature itself.

The erosion deals 1d8 points of damage per caster level to the object (hardness does not apply) to a maximum of 10d8. The maximum size of the object affected depends on your level. If you cast this spell on an object of greater size than you can affect, the spell fails.

Level	Size of Object Affected
Up to 9th	Large
10th-15th	Huge
16th-18th	Gargantuan
19th-20th	Colossal